Synchronized Streets

A “Synchronized Street” provides a high quality travel experience for travelers by enabling perfect synchronization of traffic signals in both directions of travel.

The Synchronized Street design reduces travel times and delays for travel along the street, while also improving safety for both drivers and pedestrians and enhancing accessibility. In addition, the improvement in travel operations helps transit buses stay on schedule. The design can apply in a number of contexts, including urban, suburban, and semi-rural areas.

Current RTA focus

Encourage the consideration and implementation of Synchronized Streets at appropriate locations in and connecting to the Triangle area, as both an interim and more long-term measure depending on the street context.

In cooperation with NCDOT and other transportation partners, encourage the use of the term “Synchronized Street” to improve clarity as to the purpose and benefits of this innovative street and intersection design. Note: The “Synchronized Street” design concept is sometimes known as a “superstreet” or “restricted crossing U-turn”design.

Essence of the design

All usual movements — through, left-turns, and right-turns — are permitted from the Synchronized Street at intersections with side street. However, no crossing or left-turning movements from the side street are allowed anywhere; instead, those movements turn right when entering the Synchronized Street, and then make a U-turn at a nearby crossover.

The elimination of crossing and left-turning movements from side streets allows for substantially more cycle time to be allocated to the Synchronized Street than at a conventional intersection. This also enables each travel direction to be synchronized independently, with different cycle lengths — usually lower than that found at a more conventional intersection — and different allocations of green time.

In a rural area or other locations where the design can operate effectively without the introduction of traffic signals, the street can be called a “free-flow Synchronized Street.”

Approximate capacity range

Hourly

A “typical” Synchronized Street, with 2/3 of the green time provided to the Sychronized Street through movements, will have an hourly capacity of around 1200 vehicles per lane along the Synchronized Street.

Main street U-turns at the designated crossovers — used by traffic from the side street seeking to either cross or enter the Synchronized Street — will have an hourly capacity of 600 vehicles per lane, or 1200 vehicles for two lanes, assuming they receive about 1/3 of the green time.

Main street left turns at the intersections have slightly higher hourly capacities than the Synchronized Street U-turns at the crossovers. Synchronized Street left turns also receive about 1/3 of the green time allocation.

Daily

A four lane Synchronized Street (i.e., two lanes each way) has a capacity of approximately 50,000 vehicles per day, with six and eight Synchronized Streets having daily capacities of 75,000 and 100,000 vehicles, respectively — assuming that crossing street volumes are around 25,000 vehicles per day or less.

Volumes somewhat beyond these capacity thresholds are possible if signal phasing times are reallocated (e.g., with lower crossing street volumes, more time could be given to the Synchronized Street).

By comparison, a freeway can have a capacity of up to 2400 vehicles per lane, or about twice that of a typical Synchronized Street. (A four lane freeway has a capacity of around 70,000 vehicles per day, with somewhat higher capacities possible if directional flows are balanced.)

A free-flow Synchronized Street — with no traffic signals — will have a daily capacity approaching that of a freeway.